The rebel Nusra Front in Syria appears to have gained recruits and equipment since pledging allegiance to al Qaida, according to a U.N. report released Tuesday that depicts a widening and increasingly sectarian conflict.

The more than two years of bloodshed in Syria has “accelerated radicalization,” allowing Nusra in particular to become more influential among Sunni Muslim extremist groups throughout the region, especially now that the Shiite Muslim fighters of Hezbollah are so visibly backing President Bashar Assad’s regime, the report said.

Religious and sectarian extremism is worsening on both sides as tactics grow more savage, the report said, with sharp rises in hostage taking, the use of underage combatants, sexual violence and forced displacement. The report, compiled by an international panel of inquiry on Syria for the U.N.’s Human Rights Council, covers the period from mid-January to mid-May and was based on more than 400 interviews and other evidence.

“The parties to the conflict are using dangerous rhetoric that inflames sectarian tensions and risks inciting mass, indiscriminate violence, particularly against vulnerable communities,” the report warned.

The U.N. report also said there were “reasonable grounds” to think that chemical agents had been used as weapons. But it added that “the precise agents, delivery systems or perpetrators could not be identified.”

The report’s release came only hours before France announced that tests it had conducted on samples from Syria pointed to the repeated use of the lethal nerve agent sarin, but Foreign Minister Laurent Fabius offered no details of where or by whom the gas purportedly was used, and U.S. officials said they still didn’t have enough evidence to draw a definitive conclusion.

“We need more (evidence) and we need to build on it,” White House spokesman Jay Carney said.

The language in the U.N. report was far more concrete on other aspects of the war, giving grisly, detailed accounts of the now-commonplace brutalities suffered by Syrians. At least 17 incidents that meet the definition of a massacre were recorded in the four-month period the report covers. Both parties to the conflict had carried out those and many other atrocities, the panel found.

On the regime side, there are lurid descriptions of men being rounded up arbitrarily, tortured with electrical shocks and held in vermin-infested prisons so overcrowded that detainees are forced to sleep standing up. The report also notes that the regime and its affiliated militias use sexual violence against their opponents.

Another regime tactic is “forced disappearance,” in which Syrians are seized at random, sometimes never to be heard from again or, for example, turning up among the 200 bodies that were dumped in Aleppo’s Queiq waterway.

On the anti-government side, it’s not just the Nusra Front and its fellow jihadist groups that are blamed for battlefield excesses. The U.N. report noted that rebels in general were using underage fighters in operations; at least 86 children have been killed as combatants, half of them this year alone.

The report offered no good guy-bad guy narrative – indeed, the rebels were blamed for many of the same tactics as the regime, including kidnappings, torture, arbitrary detention, looting seized homes and sectarian targeting, especially of the Alawite religious sect to which Assad and many of Syria’s elite belong.

In February, for example, unidentified rebels abducted a Sunni man in Damascus, mistaking him for an Alawite officer. He was tortured and subjected to sectarian epithets, the report said, before he finally convinced his captors that he wasn’t Alawite. He was released, but he still had to pay a ransom.

The more gruesome sectarian-tinged activity comes, however, from extremist groups such as Nusra, which the State Department has designated as a branch of the group al Qaida in Iraq. A series of recent “trials” by Islamist extremist rebels ended predictably: “Captured Alawite soldiers were consistently found guilty and executed, while non-Alawites were imprisoned or released,” witnesses told the U.N. panel.

Though facing some backlash in Syria, the Nusra Front remains popular among jihadist sympathizers and might be the reason for a noticeable recent influx of foreign volunteers, according to the U.N. report.

“Foreign fighters with jihadist inclinations, often arriving from neighboring countries, continued to reinforce its ranks,” the report said.

The panel’s report squares with the front-line observations of Elizabeth O’Bagy, an analyst with the Institute for the Study of War, who returned Saturday from spending more than two weeks observing rebel commanders in opposition-controlled Syrian territories.

O’Bagy said she’d noticed two changes in jihadist involvement since her last trip two months ago. The first was that the Nusra Front was far less popular among fellow rebel groups than before, with commanders grousing that it was a foreign-backed organization that was turning out to be more trouble than help.

The second change, O’Bagy said, was a marked increase in the number of foreign fighters – and the fact that they no longer were integrating with and being absorbed into Syrian rebel brigades. That points to the emergence of a more independent jihadist movement that might be much harder to uproot than Nusra, which was known for working in tandem with other fighting groups.

“These were fully compartmentalized units of foreign fighters that seemed to be doing their own thing, not integrating at all with the other groups,” O’Bagy said.